ISO/FDIS 20421-1

• Abstract:

  This document specifies requirements for the design, fabrication, inspection and testing of large transportable vacuum-insulated cryogenic vessels of more than 450 l volume, which are permanently (fixed tanks) or not permanently (demountable tanks and portable tanks) attached to a means of transport, for one or more modes of transport. This document applies to large transportable vacuum-insulated cryogenic vessels for fluids specified in 3.1 and does not apply to vessels designed for toxic fluids. This document does not include the general vehicle requirements, e.g. running gear, brakes, lighting, etc. NOTE 1 This document does not cover specific requirements for refillable liquid-hydrogen tanks that are primarily dedicated as fuel tanks in vehicles. For fuel tanks used in land vehicles, see ISO 13985. NOTE 2 This document does not cover specific requirements for refillable liquid hydrogen and LNG tanks that are primarily dedicated as fuel tanks in vehicles. For fuel tanks used in vehicles, see ISO 13985.

• Status: Not Published
• ICS: 23.020.40 - Cryogenic vessels
• Technical Committee: ISO/TC 220 - Cryogenic vessels
• Drafting Committee: ISO/TC 220 - Cryogenic vessels
• Current Stage: 5000 - FDIS registered for formal approval
• Start Date: 08-Jul-2026
• Completion Date: 19-Jun-2026

• Consolidates: prEN ISO 20421-1 - Cryogenic vessels - Large transportable vacuum-insulated vessels - Part 1: Design, fabrication, inspection and testing (ISO/DIS 20421-1:2025)
• Effective Date: 12-Feb-2026
• Revises: ISO 20421-1:2019 - Cryogenic vessels — Large transportable vacuum-insulated vessels — Part 1: Design, fabrication, inspection and testing
• Effective Date: 24-Jun-2023
• Revises: ISO 20421-1:2019/Amd 1:2022 - Cryogenic vessels — Large transportable vacuum-insulated vessels — Part 1: Design, fabrication, inspection and testing — Amendment 1
• Effective Date: 24-Jun-2023

Overview

ISO/FDIS 20421-1:2026 specifies the essential requirements for the design, fabrication, inspection, and testing of large transportable vacuum-insulated cryogenic vessels with a volume greater than 450 liters. Applicable to both permanently attached (fixed tanks) and non-permanently attached (demountable and portable tanks) vessels, this standard addresses those systems used for transporting non-toxic cryogenic fluids across various modes of transport. This standard is critical for manufacturers, operators, and designers to ensure safe and reliable containment of cryogenic liquids, excluding toxic substances and dedicated vehicle fuel tanks for hydrogen and LNG (see ISO 13985 for these applications).

Key Topics

• Design and Structural Requirements:
  Vessels must withstand mechanical and thermal loads, with safety validated through calculation, pressure-strengthening, or experimental methods. Designs account for operating loads, fatigue, corrosion allowance, and the mechanical integrity of both the inner vessel and the outer jacket.

• Material Selection:
  All vessel components in contact with cryogenic fluids must meet ISO 21010 compatibility requirements. Materials must also conform to toughness standards at cryogenic temperatures specified in ISO 21028-1 and ISO 21028-2, ensuring durability and safety under extreme conditions.

• Fabrication Practices:
  The standard covers critical manufacturing steps, including cutting, forming, welding (with qualification requirements), and production tolerances. Emphasis is placed on precision, cleanliness (ISO 23208), and robust welding and joining practices in compliance with referenced ISO standards.

• Inspection and Testing:
  Requirements include comprehensive quality plans, inspection stages during manufacturing, non-destructive testing methods (NDT), leakproofness, pressure testing, and rectification protocols. Acceptance criteria for welds and components are referenced in ISO 5817, ISO 10675, and related NDT standards.

• Safety Features:
  Detailed provisions for pressure relief devices (ISO 4126-2, ISO 21013 series), valves (ISO 21011), and proper marking and labelling are included to promote operational safety and compliance.

Applications

Large transportable vacuum-insulated cryogenic vessels are widely employed across industries that require the safe bulk transport of cryogenic fluids such as liquid nitrogen, oxygen, argon, or carbon dioxide. Common application areas include:

• Industrial Gas Supply and Distribution:
  Supplying hospitals, laboratories, and manufacturing facilities with large volumes of cryogenic gases.

• Food Processing and Preservation:
  Transporting large quantities of liquid nitrogen or carbon dioxide for freezing or cooling applications.

• Chemical and Pharmaceutical Industries:
  Ensuring consistent, safe delivery of cryogenic materials for controlled processes.

• Medical and Research:
  Transferring cryogenic fluids required for magnetic resonance imaging (MRI), biological storage, and research experiments.

• Energy Sector:
  Supporting processes that utilize non-toxic cryogenic gases for storage and transport.

By providing a standardized approach to vessel design and maintenance, ISO/FDIS 20421-1 supports operational reliability, regulatory compliance, and the prevention of critical failures during cryogenic fluid transport.

Related Standards

For comprehensive implementation, consider the following associated standards:

• ISO 20421-2: Operational requirements for large transportable vacuum-insulated cryogenic vessels.
• ISO 21010: Cryogenic vessels - Gas and material compatibility.
• ISO 21011: Valves for cryogenic service.
• ISO 21028-1/2: Toughness requirements for materials at cryogenic temperatures.
• ISO 23208: Cleanliness for cryogenic service.
• ISO 13985: Fuel tanks for land vehicles (hydrogen, LNG).
• ISO 3834, ISO 5817, ISO 9606 series: Quality and qualification requirements for welding.
• EN 13445-3, ASME VIII-2: Additional design references for unfired and pressure vessels.

Adopting ISO/FDIS 20421-1 ensures that large transportable cryogenic vessels meet internationally recognized safety, quality, and performance benchmarks, supporting safe and efficient bulk cryogenic fluid transport across multiple industries.

FINAL DRAFT
International
Standard
ISO/TC 220
Cryogenic vessels — Large
Secretariat: AFNOR
transportable vacuum-insulated
Voting begins on:
vessels —
2026-09-23
Part 1:
Voting terminates on:
2026-11-18
Design, fabrication, inspection and
testing
Récipients cryogéniques — Grands récipients transportables
isolés sous vide —
Partie 1: Conception, fabrication, inspection et essais
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/CEN PARALLEL PROCESSING LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 220
Cryogenic vessels — Large
Secretariat: AFNOR
transportable vacuum-insulated
Voting begins on:
vessels —
Part 1:
Voting terminates on:
Design, fabrication, inspection and
testing
Récipients cryogéniques — Grands récipients transportables
isolés sous vide —
Partie 1: Conception, fabrication, inspection et essais
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
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ii
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 5
5 General requirements . 6
6 Mechanical loads. 7
6.1 General .7
6.2 Load during the pressure test.7
7 Chemical effects . 7
8 Thermal conditions . 7
9 Materials . 8
9.1 Selection of materials .8
9.2 Inspection documentation .8
10 Design . 8
10.1 Design options .8
10.1.1 General .8
10.1.2 Design by calculation .8
10.1.3 Design by calculation and pressure strengthening .8
10.1.4 Design of components by calculation supplemented with experimental methods .9
10.2 Common design requirements .9
10.2.1 General .9
10.2.2 Design specification .9
10.2.3 Design loads .10
10.2.4 Fatigue .14
10.2.5 Corrosion allowance . 15
10.2.6 Inspection openings . 15
10.2.7 Pressure relief . 15
10.2.8 Valves .16
10.2.9 Insulation .16
10.2.10 Degree of filling .16
10.2.11 Electrical continuity .16
10.3 Design by calculation .16
10.3.1 General .16
10.3.2 Inner vessel .16
10.3.3 Outer jacket .19
10.3.4 Attachments . 20
10.3.5 Piping and accessories . 20
10.3.6 Calculation formula. 20
10.3.7 Calculations for operating loads . 44
11 Fabrication .44
11.1 General . 44
11.2 Cutting . .45
11.3 Cold forming .45
11.3.1 Austenitic stainless steel .45
11.3.2 Ferritic steel .45
11.3.3 Aluminium or aluminium alloy . 46
11.4 Hot forming. 46
11.4.1 General . 46
11.4.2 Austenitic stainless steel . 46
11.4.3 Ferritic steel . 46

iii
11.4.4 Aluminium or aluminium alloy .47
11.5 Manufacturing tolerances .47
11.5.1 General .47
11.5.2 Plate alignment .47
11.5.3 Thickness . 48
11.5.4 Dished ends . 48
11.5.5 Cylinders . 48
11.6 Welding . .51
11.6.1 General .51
11.6.2 Qualification .51
11.6.3 Temporary attachments .51
11.6.4 Welded joints .51
11.7 Non-welded joints .52
12 Inspection and testing .52
12.1 Quality plan .52
12.1.1 General .52
12.1.2 Inspection stages during manufacture of an inner vessel .52
12.1.3 Additional inspection stages during manufacture of a large transportable
cryogenic vessel . 53
12.2 Production control test plates . 53
12.2.1 Requirements . 53
12.2.2 Extent of testing . 53
12.3 Non-destructive testing . 54
12.3.1 General . 54
12.3.2 Extent of examination for surface imperfections . 54
12.3.3 Extent of examination for inner-vessel weld seams . 55
12.3.4 Acceptance criteria for surface and volumetric imperfections as classified in
ISO 6520-1 . 55
12.4 Rectification . 56
12.5 Pressure testing . 56
13 Marking and labelling .57
14 Final acceptance test .57
15 Periodic inspection .57
16 Documentation .57
Annex A (informative) Examples of tank plates .59
Annex B (informative) Elastic stress analysis .62
Annex C (normative) Additional requirements for 9 % Ni steel .70
Annex D (normative) Pressure strengthening of vessels from austenitic stainless steels .72
Annex E (informative) Specific weld details .86
Annex F (normative) Outer-jacket relief devices .89
Annex G (informative) Base materials .90
Annex H (informative) Components subject to external pressure (pressure on the convex
surface) — Calculation.99
Annex I (informative) Design of openings in cylinders, spheres and cones — Calculation .106
Annex J (normative) Reference material and equivalent thickness .111
Annex K (informative) Refrigerated liquefied gases .113
Bibliography .114

iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO’s adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 220, Cryogenic vessels, in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 268, Cryogenic vessels
and specific hydrogen technologies applications, in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 20421-1:2019), which has been technically
revised. It also incorporates the Amendment ISO 20421-1:2019/Amd 1:2022.
The main changes are as follows:
— 12.3 has been revised;
— correction of load factors for normal operation for fatigue analysis in specified transportation modes in
Table 2;
— in 10.2.3.11, loads for piping and valves divided for road/water and rail condition;
— correction of Table 3;
— in 10.3.2.3.1, correction of used Material property K for the calculations under consideration of ADR/
RID/IMDG-Code/49CFR;
— material Table D.1 splitting in European Material Table D.1 and Non-European Material Table D.2;
— correction of requirements for testing plates under consideration of cold strengthening in Table D.3;
— correction of Table J.1 under consideration of ADR/RID/IMDG-Code/49CFR.
A list of all parts in the ISO 20421 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
FINAL DRAFT International Standard ISO/FDIS 20421-1:2026(en)
Cryogenic vessels — Large transportable vacuum-insulated
vessels —
Part 1:
Design, fabrication, inspection and testing
1 Scope
This document specifies requirements for the design, fabrication, inspection and testing of large
transportable vacuum-insulated cryogenic vessels of more than 450 l volume, which are permanently (fixed
tanks) or not permanently (demountable tanks and portable tanks) attached to a means of transport, for one
or more modes of transport.
This document applies to large transportable vacuum-insulated cryogenic vessels for fluids and does not
apply to vessels designed for toxic fluids.
This document does not specify general vehicle requirements, e.g. running gear, brakes, lighting.
NOTE This document does not cover specific requirements for refillable liquid hydrogen and liquified natural gas
(LNG) tanks that are primarily dedicated as fuel tanks in vehicles. For fuel tanks used in vehicles, see ISO 13985.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 3834-2, Quality requirements for fusion welding of metallic materials — Part 2: Comprehensive quality
requirements
ISO 4126-2, Safety devices for protection against excessive pressure — Part 2: Bursting disc safety devices
ISO 5817, Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) —
Quality levels for imperfections
ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels
ISO 9606-2, Qualification test of welders — Fusion welding — Part 2: Aluminium and aluminium alloys
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO 10042, Welding — Arc-welded joints in aluminium and its alloys — Quality levels for imperfections
ISO 10474:2013, Steel and steel products — Inspection documents
ISO 10675-1, Non-destructive testing of welds — Acceptance levels for radiographic testing — Part 1: Steel,
nickel, titanium and their alloys
ISO 10675-2, Non-destructive testing of welds — Acceptance levels for radiographic testing — Part 2: Aluminium
and its alloys
ISO 14732, Welding personnel — Qualification testing of welding operators and weld setters for mechanized and
automatic welding of metallic materials

ISO 15613, Specification and qualification of welding procedures for metallic materials — Qualification based
on a pre-production welding test
ISO 15614-1, Specification and qualification of welding procedures for metallic materials — Welding procedure
test — Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys
ISO 15614-2, Specification and qualification of welding procedures for metallic materials — Welding procedure
test — Part 2: Arc welding of aluminium and its alloys
ISO 17635, Non-destructive testing of welds — General rules for metallic materials
ISO 17637, Non-destructive testing of welds — Visual testing of fusion-welded joints
ISO 20421-2, Cryogenic vessels — Large transportable vacuum-insulated vessels — Part 2: Operational
requirements
ISO 21010, Cryogenic vessels — Gas/material compatibility
ISO 21011, Cryogenic vessels — Valves for cryogenic service
ISO 21028-1, Cryogenic vessels — Toughness requirements for materials at cryogenic temperature — Part 1:
Temperatures below -80 °C
ISO 21028-2, Cryogenic vessels — Toughness requirements for materials at cryogenic temperature — Part 2:
Temperatures between ‒80 degrees C and ‒20 degrees C
ISO 21013-1, Cryogenic vessels — Pressure-relief accessories for cryogenic service — Part 1: Reclosable pressure-
relief valves
ISO 21013-2, Cryogenic vessels — Pressure-relief accessories for cryogenic service — Part 2: Non-reclosable
pressure-relief devices
ISO 21013-3, Cryogenic vessels — Pressure-relief accessories for cryogenic service — Part 3: Sizing and capacity
determination
ISO 23208, Cryogenic vessels — Cleanliness for cryogenic service
ISO 17636-1, Non-destructive testing of welds — Radiographic testing — Part 1: X- and gamma-ray techniques
with film
ISO 23277, Non-destructive testing of welds — Penetrant testing — Acceptance levels
ASME VIII-2, Rules for construction of pressure vessels, Division 2, Alternative Rules
EN 13445-3, Unfired pressure vessels — Part 3: Design
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
cryogenic fluid
gas which is partially liquid because of its low temperature
Note 1 to entry: This includes totally evaporated liquids and supercritical fluids.
Note 2 to entry: In the context of this document, the refrigerated but non-toxic gases and gas mixtures given in
Table K.1 are referred to as cryogenic fluids.

3.2
large transportable cryogenic vessel
thermally insulated vessel of more than 450 l intended for the transport of one or more cryogenic fluids (3.1),
consisting of an inner vessel (3.4), an outer jacket (3.5), all of the valves and service equipment (3.9) together
with the structural parts
Note 1 to entry: The large transportable cryogenic vessel comprises a complete assembly that is ready for service.
Note 2 to entry: Large transportable cryogenic vessels are equivalent to large transportable cryogenic tanks.
3.3
insulation
vacuum interspace between the inner vessel (3.4) and the outer jacket (3.5)
Note 1 to entry: The space can be filled with material to reduce the heat transfer between the inner vessel and the
outer jacket.
3.4
inner vessel
pressure (3.16) vessel intended to contain the cryogenic fluid (3.1) to be transported
3.5
outer jacket
gas-tight enclosure which contains the inner vessel (3.4) and enables the vacuum to be established
3.6
normal operation
intended operation of the vessel at a pressure (3.16) not greater than the maximum allowable working pressure
(3.20) including the handling loads
3.7
operating load
load exerted on the transportable cryogenic vessel in all normal conditions of transport including loading,
unloading, moving and lifting
3.8
piping system
all pipes, tubes and associated components which can come in contact with cryogenic fluids (3.1) including
valves, fittings, pressure-relief devices and their supports
3.9
service equipment
measuring instruments and filling, discharge, venting, safety, heating, cooling and insulating devices
including any equipment for storing cooling fluids
3.10
manufacturer
company that carries out the final assembly, including the final
acceptance test, of the large transportable cryogenic vessel (3.2)
3.11
gross volume
internal volume of the inner vessel (3.4), excluding nozzles, pipes, etc., determined at
minimum design temperature and atmospheric pressure (3.16)
3.12
tare mass
mass of the empty large transportable cryogenic vessel (3.2)

3.13
net volume
volume of the inner vessel (3.4), below the inlet to the relief devices, excluding nozzles, pipes, etc., determined
at minimum design temperature and atmospheric pressure (3.16)
3.14
net mass
maximum allowable mass of the cryogenic fluid (3.1) which may be filled
Note 1 to entry: The maximum allowable mass is equal to the mass of the cryogenic liquid occupying 98 % of the net
volume (3.13) of the inner vessel (3.4) under conditions of incipient opening of the relief device with the vessel in a level
attitude and the mass of the gas at the same conditions in the remaining volume of the inner vessel.
Note 2 to entry: Cryogenic liquid helium can occupy 100 % of the volume of the inner vessel at any pressure (3.16).
3.15
gross mass
sum of tare mass (3.12) and net mass (3.14)
3.16
pressure
gauge pressure
pressure relative to atmospheric pressure
3.17
fixed tank
large transportable (cryogenic) vessel having a capacity of more than 1 000 litres which is permanently
attached to a vehicle (which then becomes a tank-vehicle) or is an integral part of the frame of such vehicle
3.18
demountable tank
large transportable vessel non-permanently attached to a vehicle
Note 1 to entry: When attached to the carrier vehicle, the demountable tank meets the requirements prescribed for a
fixed tank (3.17). It is designed to be lifted only when empty.
3.19
portable tank
thermally insulated multimodal tank having a capacity of more than 450 litres fitted with service equipment
(3.9) and structural equipment necessary for the carriage of refrigerated liquefied gases
Note 1 to entry: It can be lifted full and loaded and discharged without removal of structural element.
Note 2 to entry: The list of the refrigerated liquefied gases is available in Annex K.
3.20
maximum allowable working pressure
p
s
maximum gauge pressure (3.16) permissible at the top of the vessel in its normal operating position
3.21
relief plate
relief plug
plate or plug retained by atmospheric pressure (3.16) which allows relief of excess internal pressure,
generally from the vacuum jacket
3.22
bursting disc device
non-reclosing pressure-relief device ruptured by differential pressure (3.16)
Note 1 to entry: It is the complete assembly of installed components including the bursting disc holder, where
appropriate.
3.23
pressure-strengthened vessel
pressure vessel which has been subjected to a calculated and controlled internal pressure (strengthening
pressure) after completion, the wall thickness of which is calculated on the basis of the stress at the
strengthening pressure and not on the basis of the conventional design stress value of the material used
Note 1 to entry: Pressure (3.16) vessels made from solution heat-treated material are subject to a controlled plastic
deformation during the strengthening operation as its yield point is raised. Pressure vessels made from work-hardened
material are subject to little or no plastic deformation.
3.24
residual elongation
original elongation of the steel minus the elongation created by the cold-forming deformation
3.25
leakproofness test
test using gas subjecting the shell and its service equipment (3.9), to an effective internal pressure (3.16) not
less than 90 % of the maximum allowable working pressure but not greater than the design pressure
4 Symbols
Symbol Definition Unit
b width of pad, ring or shell reinforcement mm
c allowance for corrosion mm
d distance mm
d diameter of opening mm
i
d outside diameter of tube or nozzle mm
a
f narrow side of rectangular or elliptical plate mm
l cone length between effective stiffenings (see Figure 5) mm
c
l ligament (web) between two nozzles mm
l l′ buckling length mm
b, b
l length of nozzle reinforcement outstanding mm
s
n number of lobes —
p design pressure as defined in 10.3.2.2 —
p calculation pressure as defined in 10.2.3.2.1 a) bar
c
p allowable external pressure limited by elastic buckling bar
e
p strengthening pressure bar
k
p liquid pressure bar
L
p allowable external pressure limited by plastic deformation bar
p
p maximum allowable gauge pressure bar
s
p test pressure (see 6.2) bar
T
r radius, e.g. inside knuckle radius of dished end and cones mm
s minimum thickness mm
s required wall thickness at opening edge mm
A
s actual wall thickness mm
e
s required wall thickness outside corner area mm
g
s thickness of nozzle reinforcement in stand mm
n
s wall thickness of nozzle mm
s
s required wall thickness within corner area mm
t in this context, centre-to-centre distance between two nozzles mm
x (decay-length zone) distance over which governing stress is assumed to act mm

Symbol Definition Unit
x characteristic lengths (i = 1,2,3) to define corner area [Figure 10 a) and mm
i
Figure 10 b) and 10.3.6.5.4]
η factor indicative of the utilization of the permissible design stress in joints or —
factor allowing for weakenings
A cross-sectional area of reinforcing element mm
C, β design factors —
D shell diameter mm
D outside diameter, e.g. of a cylindrical shell mm
a
D outside diameter of connected cylinder (see Figure 10) mm
a1
D outside diameter at effective stiffening (see Figure 12) mm
a2
D internal diameter, e.g. of a cylindrical shell mm
i
D design diameter (see Figure 10) mm
k
D shell diameter at nozzle (see Figure 11) mm
s
E Young’s modulus N/mm
G Gravity point —
I moment of inertia of reinforcing element mm
R minimum guaranteed yield stress or 0,2 % proof stress at 20 °C (1 % proof N/mm
e
stress for austenitic steel)
R minimum guaranteed tensile strength at 20 °C N/mm
m
R minimum guaranteed yield strength with 1,0 % plastic deformation N/mm
p1,0
K material property used for design (see 10.3.2.3) N/mm
K material property at temperature T in °C (e.g. K for material property at 20 °C N/mm
T 20
(see 10.3.2.3.2)
R radius of curvature, e.g. inside crown radius of dished end mm
S safety factor at design pressure, in relation with R —
e
S safety factor against elastic buckling at design pressure —
k
S safety factor against plastic deformation —
p
Z auxiliary value —
v Poisson’s ratio —
u out of roundness (see 11.5.5.2) —
φ cone angle °
σ design stress value (strengthening stress value in Annex D) N/mm
k
5 General requirements
5.1 Large transportable cryogenic vessels shall safely withstand the mechanical and thermal loads and the
chemical effects encountered during pressure test and normal operation. These requirements are deemed
to be satisfied if Clauses 6 to 12 are fulfilled. The vessel shall be marked in accordance with Clause 13, tested
in accordance with Clause 14 and operated in accordance with ISO 20421-2.
5.2 Large transportable cryogenic vessels shall be configured in such a way that the vessel can be operated
safely (e.g. valves, pressure-relief devices). The number of openings in the inner vessel for this equipment
shall be kept to a minimum.
5.3 Large transportable cryogenic vessel shall be clean for the intended service in accordance with
ISO 23208.
5.4 The manufacturer shall retain the documents referred to in Clause 16, and all supporting
documentation (including that from his subcontractors, if any), for a required period (e.g. product liability).

In addition, the manufacturer shall retain all supporting and background documentation (including that
from his subcontractors, if any) which establishes that the vessel conforms to this document.
6 Mechanical loads
6.1 General
The large transportable cryogenic vessel shall resist the mechanical loads mentioned in 10.2.3 without such
deformation which can affect safety and which can lead to leakage. This requirement can be validated by:
— the calculation;
— the calculation and pressure-strengthening method, if allowed;
— the calculation and experimental method.
6.2 Load during the pressure test
The load exerted during the pressure test shall be calculated with Formula (1):
pp13, 1  (1)

Ts
where
p is the test pressure (in bar);
T
P is the maximum allowable pressure (in bar);
s
+1 is the allowance for external vacuum (in bar).
7 Chemical effects
Due to operating temperatures and the materials of construction, the possibility of chemical action on the
inner surfaces in contact with the cryogenic fluids can be neglected.
Due to the fact that the inner vessel is inside an evacuated outer jacket, neither external corrosion of the inner
vessel, nor corrosion on the inner surfaces of the outer jacket will occur. Therefore, inspection openings are
not required in the inner vessel or the outer jacket.
Corrosion allowance is also not required on surfaces in contact with the operating fluid or exposed to the
vacuum interspace between the inner vessel and the outer jacket.
The material and the protection for the surfaces exposed to the atmosphere shall be suitable for intended
use (e.g. resistant to industrial and marine atmospheres).
8 Thermal conditions
The following thermal conditions shall be taken into account:
— for the inner vessel and its associated equipment, the full range of temperature expected;
— for the outer jacket and equipment thereof (other than equipment covered in Clause 7):
— a minimum working temperature of −20 °C;
— a maximum working temperature of 50 °C.
NOTE 1 Some locations require lower minimum working temperature e.g. –40 °C and/or higher maximum working
temperature, e.g. +65 °C.
NOTE 2 This does not apply if the jacket is designed for a lower temperature to be marked on the nameplate.

9 Materials
9.1 Selection of materials
9.1.1 Materials which are, or can be, in contact with cryogenic fluids shall be in accordance with ISO 21010.
9.1.2 Materials used at low temperatures shall follow the requirements of the relevant clauses of
ISO 21028-1 and ISO 21028-2; for non-metallic materials, low-temperature suitability shall be validated by
an experimental method, taking into account operating temperatures.
9.1.3 The base materials, listed in Annex G, subject to meeting the extra requirements given in Clauses 5
to 16, are suitable for and may be employed in the manufacture of the cryogenic vessels, in conformance
with this document.
9.2 Inspection documentation
9.2.1 The material according to ISO 21028-1 and ISO 21028-2 shall be declared by an inspection certificate
3.1 in accordance with ISO 10474:2013, 5.1.
9.2.2 The material manufactured to a recognized International Standard shall meet the testing
requirements of ISO 21028-1 and ISO 21028-2 and shall be declared by an inspection certificate 3.1 in
accordance with ISO 10474:2013, 5.1.
9.2.3 The delivery of material which is not manufactured to a recognized In
...

ISO/DISFDIS 20421-1:2026(en)
ISO/TC 220/WG 1
Secretariat: AFNOR
Date: 2026-06-2909-03
Cryogenic vessels — Large transportable vacuum-insulated
vessels —
Part 1:
Design, fabrication, inspection and testing
Récipients cryogéniques — RécipientsGrands récipients transportables isolés sous vide de grande
contenance — —
Partie 1: Conception, fabrication, inspection et essais
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ISO/DISFDIS 20421-1:2026(en)
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of
this publication may be reproduced or utilized otherwise in any form or by any means, electronic or
mechanical, including photocopying, or posting on the internet or an intranet, without prior written
permission. Permission can be requested from either ISO at the address below or ISO’sISO's member body
in the country of the requester.
ISO copyright officeCopyright Office
CP 401 • Ch. de Blandonnet 8
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Phone: + 41 22 749 01 11
Email: [e-mail] [e-mail]
Website: www.iso.org
Published in Switzerland.
ii
ISO/DISFDIS 20421-1:2026(en)
Contents
Foreword . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 5
5 General requirements . 7
6 Mechanical loads . 7
6.1 General . 7
6.2 Load during the pressure test . 8
7 Chemical effects . 8
8 Thermal conditions . 8
9 Materials . 8
9.1 Selection of materials . 8
9.2 Inspection documentation . 9
10 Design . 9
10.1 Design options . 9
10.1.1 General . 9
10.1.2 Design by calculation . 9
10.1.3 Design by calculation and pressure strengthening . 9
10.1.4 Design of components by calculation supplemented with experimental methods . 9
10.2 Common design requirements . 10
10.2.1 General . 10
10.2.2 Design specification . 10
10.2.3 Design loads . 11
10.2.4 Fatigue . 16
10.2.5 Corrosion allowance . 16
10.2.6 Inspection openings . 16
10.2.7 Pressure relief . 16
10.2.8 Valves . 17
10.2.9 Insulation . 17
10.2.10 Degree of filling . 17
10.2.11 Electrical continuity . 17
10.3 Design by calculation . 18
10.3.1 General . 18
10.3.2 Inner vessel . 18
iii
ISO/DISFDIS 20421-1:2026(en)
10.3.3 Outer jacket . 20
10.3.4 Attachments . 21
10.3.5 Piping and accessories . 21
10.3.6 Calculation formula . 21
10.3.7 Calculations for operating loads . 60
11 Fabrication . 61
11.1 General . 61
11.2 Cutting . 61
11.3 Cold forming . 61
11.3.1 Austenitic stainless steel . 61
11.3.2 Ferritic steel . 62
11.3.3 Aluminium or aluminium alloy . 63
11.4 Hot forming . 63
11.4.1 General . 63
11.4.2 Austenitic stainless steel . 63
11.4.3 Ferritic steel . 63
11.4.4 Aluminium or aluminium alloy . 63
11.5 Manufacturing tolerances . 63
11.5.1 General . 63
11.5.2 Plate alignment . 64
11.5.3 Thickness . 66
11.5.4 Dished ends . 66
11.5.5 Cylinders . 66
11.6 Welding . 69
11.6.1 General . 69
11.6.2 Qualification . 70
11.6.3 Temporary attachments . 70
11.6.4 Welded joints . 70
11.7 Non-welded joints . 71
12 Inspection and testing . 71
12.1 Quality plan . 71
12.1.1 General . 71
12.1.2 Inspection stages during manufacture of an inner vessel . 71
12.1.3 Additional inspection stages during manufacture of a large transportable cryogenic
vessel 72
12.2 Production control test plates . 72
12.2.1 Requirements . 72
iv
ISO/DISFDIS 20421-1:2026(en)
12.2.2 Extent of testing . 72
12.3 Non-destructive testing . 74
12.3.1 General . 74
12.3.2 Extent of examination for surface imperfections . 74
12.3.3 Extent of examination for inner-vessel weld seams . 74
12.3.4 Acceptance criteria for surface and volumetric imperfections as classified in
ISO 6520-1 . 75
12.4 Rectification . 76
12.5 Pressure testing . 76
13 Marking and labelling . 77
14 Final acceptance test . 77
15 Periodic inspection . 77
16 Documentation . 77
Annex A (informative) Examples of tank plates . 79
Annex B (informative) Elastic stress analysis . 83
Annex C (normative) Additional requirements for 9 % Ni steel . 94
Annex D (normative) Pressure strengthening of vessels from austenitic stainless steels . 96
Annex E (informative) Specific weld details . 110
Annex F (normative) Outer-jacket relief devices . 115
Annex G (informative) Base materials . 116
Annex H (informative) Components subject to external pressure (pressure on the convex
surface) — Calculation . 126
Annex I (informative) Design of openings in cylinders, spheres and cones — Calculation . 136
Annex J (normative) Reference material and equivalent thickness . 143
Annex K (informative) Refrigerated liquefied gases . 145
Bibliography . 146

v
ISO/DISFDIS 20421-1:2026(en)
PageForeword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of
(a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned
that this may not represent the latest information, which may be obtained from the patent database
available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent
rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO'sISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT)), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 220, Cryogenic vessels, in collaboration
with the European Committee for Standardization (CEN) Technical Committee CEN/TC 268, Cryogenic
vessels and specific hydrogen technologies applications, in accordance with the Agreement on technical
cooperation between ISO and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 20421-1:2019), which has been
technically revised. It also incorporates the Amendment ISO 20421-1:2019/Amd 1:2022.
The main changes compared to the previous edition are as follows:
— 12.3 has been revised;
— Correctioncorrection of load factors for normal operation for fatigue analysis in specified
transportation modes in Table 2;
— in 10.2.3.11, loads for piping and valves divided for road/water and rail condition;
— correction of Table 3;
— in 10.3.2.3.1, correction of used Material property K for the calculations under consideration of
ADR/RID/IMDG-Code/49CFR;
vi
ISO/DISFDIS 20421-1:2026(en)
— Materialmaterial Table D.1 splitting in European Material Table D.1 and Non-European Material
Table D.2;
— Correctioncorrection of Requirementsrequirements for Testingtesting plates under consideration of
cold strengthening in Table D.3;
— Subclause J.3 Correction— correction of Table J.1 under consideration of ADR/RID/IMDG-
Code/49CFR.
A list of all parts in the ISO 20421 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
vii
FINAL DRAFT International Standard ISO/FDIS 20421-1:2026(en)

Cryogenic vessels — Large transportable vacuum insulated
vessels — Part 1: Design, fabrication, inspection and testing
1 Scope
This document specifies requirements for the design, fabrication, inspection and testing of large
transportable vacuum-insulated cryogenic vessels of more than 450 l volume, which are permanently
(fixed tanks) or not permanently (demountable tanks and portable tanks) attached to a means of
transport, for one or more modes of transport.
This document applies to large transportable vacuum-insulated cryogenic vessels for fluids and does not
apply to vessels designed for toxic fluids.
This document does not specify general vehicle requirements, e.g. running gear, brakes, lighting, etc.
NOTE This document does not cover specific requirements for refillable liquid hydrogen and liquified natural
gas (LNG) tanks that are primarily dedicated as fuel tanks in vehicles. For fuel tanks used in vehicles, see ISO 13985.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3834-2, Quality requirements for fusion welding of metallic materials — Part 2: Comprehensive quality
requirements
ISO 4126-2, Safety devices for protection against excessive pressure — Part 2: Bursting disc safety devices
ISO 5817, Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding
excluded) — Quality levels for imperfections
ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels
ISO 9606-2, Qualification test of welders — Fusion welding — Part 2: Aluminium and aluminium alloys
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO 10042, Welding — Arc-welded joints in aluminium and its alloys — Quality levels for imperfections
ISO 10474:2013, Steel and steel products — Inspection documents
ISO 10675-1, Non-destructive testing of welds — Acceptance levels for radiographic testing — Part 1: Steel,
nickel, titanium and their alloys
ISO 10675--2, Non-destructive testing of welds — Acceptance levels for radiographic testing — Part 2:
Aluminium and its alloys
ISO 14732, Welding personnel — Qualification testing of welding operators and weld setters for
mechanized and automatic welding of metallic materials
ISO 15613, Specification and qualification of welding procedures for metallic materials — Qualification
based on a pre-production welding test
ISO 15614-1, Specification and qualification of welding procedures for metallic materials — Welding
procedure test — Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys
ISO 15614-2, Specification and qualification of welding procedures for metallic materials — Welding
procedure test — Part 2: Arc welding of aluminium and its alloys
ISO 17635, Non-destructive testing of welds — General rules for metallic materials
ISO 17637, Non-destructive testing of welds — Visual testing of fusion-welded joints
ISO 20421-2, Cryogenic vessels — Large transportable vacuum-insulated vessels — Part 2: Operational
requirements
ISO 21010, Cryogenic vessels — Gas/material compatibility
ISO 21011, Cryogenic vessels — Valves for cryogenic service
ISO 21028-1, Cryogenic vessels — Toughness requirements for materials at cryogenic temperature —
Part 1: Temperatures below -80 degrees °C
ISO 21028-2, Cryogenic vessels — Toughness requirements for materials at cryogenic temperature —
Part 2: Temperatures between -‒80 degrees C and -‒20 degrees C
ISO 21013-1, Cryogenic vessels — Pressure-relief accessories for cryogenic service — Part 1: Reclosable
pressure-relief valves
ISO 21013-2, Cryogenic vessels — Pressure-relief accessories for cryogenic service — Part 2: Non-reclosable
pressure-relief devices
ISO 21013-3, Cryogenic vessels — Pressure-relief accessories for cryogenic service — Part 3: Sizing and
capacity determination
ISO 23208, Cryogenic vessels — Cleanliness for cryogenic service
Non-destructive testing of welds — Radiographic testing — Part 1: X- and gamma-ray
ISO 17636--1,
techniques with film ISO 3452-1, Non-destructive testing — Penetrant testing — Part 1: General principles
ISO 23277, Non-destructive testing of welds — Penetrant testing — Acceptance levels
ASME VIII-2, Rules for construction of pressure vessels, Division 2, Alternative Rules
EN 13445-3, Unfired pressure vessels — Part 3: Design
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological terminology databases for use in standardization at the following
addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
cryogenic fluid
gas which is partially liquid because of its low temperature
Note 1 to entry: This includes totally evaporated liquids and supercritical fluids.
Note 2 to entry: In the context of this document, the refrigerated but non-toxic gases and gas mixtures given in
Table K.1 are referred to as cryogenic fluids.
3.2
large transportable cryogenic vessel
thermally insulated vessel of more than 450 l intended for the transport of one or more cryogenic fluids
(3.1), consisting of an inner vessel (3.4), an outer jacket (3.5), all of the valves and service equipment (3.9)
together with the structural parts
Note 1 to entry: The large transportable cryogenic vessel comprises a complete assembly that is ready for service.
Note 2 to entry: Large transportable cryogenic vessels are equivalent to large transportable cryogenic tanks.
3.3
insulation
vacuum interspace between the inner vessel (3.4) and the outer jacket (3.5)
Note 1 to entry: The space can be filled with material to reduce the heat transfer between the inner vessel and the
outer jacket.
3.4
inner vessel
pressure (3.16) vessel intended to contain the cryogenic fluid (3.1) to be transported
3.5
outer jacket
gas-tight enclosure which contains the inner vessel (3.4) and enables the vacuum to be established
3.6
normal operation
intended operation of the vessel at a pressure (3.16) not greater than the maximum allowable working
pressure (3.20) including the handling loads (3.7)
3.7
operating load
load exerted on the transportable cryogenic vessel in all normal conditions of transport including loading,
unloading, moving and lifting
3.8
piping system
all pipes, tubes and associated components which can come in contact with cryogenic fluids (3.1)
including valves, fittings, pressure-relief devices and their supports
3.9
service equipment
measuring instruments and filling, discharge, venting, safety, heating, cooling and insulating devices
including any equipment for storing cooling fluids
3.10
manufacturer
company that carries out the final assembly, including the final
acceptance test, of the large transportable cryogenic vessel (3.2)
3.11
gross volume
internal volume of the inner vessel (3.4), excluding nozzles, pipes, etc., determined
at minimum design temperature and atmospheric pressure (3.16)
3.12
tare mass
mass of the empty large transportable cryogenic vessel (3.2)
3.13
net volume
volume of the inner vessel (3.4), below the inlet to the relief devices, excluding nozzles, pipes, etc.,
determined at minimum design temperature and atmospheric pressure (3.16)
3.14
net mass
maximum allowable mass of the cryogenic fluid (3.1) which may be filled
Note 1 to entry: The maximum allowable mass is equal to the mass of the cryogenic liquid occupying 98 % of the
net volume (3.13) of the inner vessel (3.4) under conditions of incipient opening of the relief device with the vessel
in a level attitude and the mass of the gas at the same conditions in the remaining volume of the inner vessel.
Note 2 to entry: Cryogenic liquid helium can occupy 100 % of the volume of the inner vessel at any pressure (3.16).
3.15
gross mass
sum of tare mass (3.12) plus and net mass (3.14)
3.16
pressure
gauge pressure
pressure relative to atmospheric pressure
3.17
fixed tank
large transportable (cryogenic) vessel having a capacity of more than 1 000 litres which is permanently
attached to a vehicle (which then becomes a tank-vehicle) or is an integral part of the frame of such
vehicle 3.18
3.18
demountable tank
large transportable vessel non-permanently attached to a vehicle
Note 1 to entry: When attached to the carrier vehicle, the demountable tank meets the requirements prescribed for
a fixed tank (3.17). It is designed to be lifted only when empty.
3.19
portable tank
thermally insulated multimodal tank having a capacity of more than 450 litres fitted with service
equipment (3.9) and structural equipment necessary for the carriage of refrigerated liquefied gases
Note 1 to entry: It can be lifted full and loaded and discharged without removal of structural element.
Note 2 to entry: The list of the refrigerated liquefied gases is available in Annex K.
3.20
maximum allowable working pressure
p
s
maximum gauge pressure (3.16) permissible at the top of the vessel in its normal operating position
3.21
relief plate
relief plug
plate or plug retained by atmospheric pressure (3.16) which allows relief of excess internal pressure,
generally from the vacuum jacket
3.22
bursting disc device
non-reclosing pressure-relief device ruptured by differential pressure (3.16)
Note 1 to entry: It is the complete assembly of installed components including the bursting disc holder, where
appropriate.
3.23
pressure-strengthened vessel
pressure vessel which has been subjected to a calculated and controlled internal pressure (strengthening
pressure) after completion, the wall thickness of which is calculated on the basis of the stress at the
strengthening pressure and not on the basis of the conventional design stress value of the material used
Note 1 to entry: Pressure (3.16) vessels made from solution heat-treated material are subject to a controlled plastic
deformation during the strengthening operation as its yield point is raised. Pressure vessels made from
work-hardened material are subject to little or no plastic deformation.
3.24
residual elongation
original elongation of the steel minus the elongation created by the cold-forming deformation
3.25
leakproofness test
test using gas subjecting the shell and its service equipment (3.9), to an effective internal pressure (3.16)
not less than 90 % of the maximum allowable working pressure but not greater than the design pressure
4 Symbols
Symbol Definition Unit
b width of pad, ring or shell reinforcement mm
c allowance for corrosion mm
d distance mm
d diameter of opening mm
i
d outside diameter of tube or nozzle mm
a
f narrow side of rectangular or elliptical plate mm
lc cone length between effective stiffenings (see Figure 5) mm
l ligament (web) between two nozzles mm
lb, l′b buckling length mm
l length of nozzle reinforcement outstanding mm
s
n number of lobes —
p design pressure as defined in 10.3.2.2 —
pc calculation pressure as defined in 10.2.3.2.1 a) bar
p allowable external pressure limited by elastic buckling bar
e
pk strengthening pressure bar
pL liquid pressure bar
p allowable external pressure limited by plastic deformation bar
p
p maximum allowable gauge pressure bar
s
pT test pressure (see 6.2) bar
r radius, e.g. inside knuckle radius of dished end and cones mm
s minimum thickness mm
s required wall thickness at opening edge mm
A
se actual wall thickness mm
sg required wall thickness outside corner area mm
s thickness of nozzle reinforcement in stand mm
n
Ssss wall thickness of nozzle mm
s1 required wall thickness within corner area mm
t in this context, centre-to-centre distance between two nozzles mm
x (decay-length zone) distance over which governing stress is assumed to act mm
xi characteristic lengths (i = 1,2,3) to define corner area [Figure 10 a) and mm
Figure 10 b) and 10.3.6.5.4]
η factor indicative of the utilization of the permissible design stress in joints or —
factor allowing for weakenings
A cross-sectional area of reinforcing element mm
C, β design factors —
D shell diameter mm
Da outside diameter, e.g. of a cylindrical shell mm
Da1 outside diameter of connected cylinder (see Figure 10) mm
D outside diameter at effective stiffening (see Figure 12) mm
a2
D internal diameter, e.g. of a cylindrical shell mm
i
Dk design diameter (see Figure 10) mm
Ds shell diameter at nozzle (see Figure 11) mm
E Young’s modulus N/mm
G Gravity point —
I moment of inertia of reinforcing element mm
R minimum guaranteed yield stress or 0,2 % proof stress at 20 °C (1 % proof N/mm
e
stress for austenitic steel)
Rm minimum guaranteed tensile strength at 20 °C N/mm
Rp1,0 minimum guaranteed yield strength with 1,0 % plastic deformation N/mm
K material property used for design (see 10.3.2.3) N/mm
K material property at temperature T in °C (e.g. K for material property at N/mm
T 20
20 °C (see 10.3.2.3.2)
R radius of curvature, e.g. inside crown radius of dished end mm
S safety factor at design pressure, in relation with R —
e
Sk safety factor against elastic buckling at design pressure —
Sp safety factor against plastic deformation —
Z auxiliary value —
v Poisson’s ratio —
u out of roundness (see 11.5.5.2) —
φ cone angle °
σ design stress value (strengthening stress value in Annex D) N/mm
k
5 General requirements
5.1 Large transportable cryogenic vessels shall safely withstand the mechanical and thermal loads and
the chemical effects encountered during pressure test and normal operation. These requirements are
deemed to be satisfied if Clauses 6 to 12 are fulfilled. The vessel shall be marked in accordance with
Clause 13, tested in accordance with Clause 14 and operated in accordance with ISO 20421-2.
5.2 Large transportable cryogenic vessels shall be configured in such a way that the vessel can be
operated safely (e.g. valves, pressure-relief devices). The number of openings in the inner vessel for this
equipment shall be kept to a minimum.
5.3 Large transportable cryogenic vessel shall be clean for the intended service in accordance with
ISO 23208.
5.4 The manufacturer shall retain the documents referred to in Clause 16, and all supporting
documentation (including that from his subcontractors, if any), for a required period (e.g. product
liability). In addition, the manufacturer shall retain all supporting and background documentation
(including that from his subcontractors, if any) which establishes that the vessel conforms to this
document.
6 Mechanical loads
6.1 General
The large transportable cryogenic vessel shall resist the mechanical loads mentioned in 10.2.3 without
such deformation which can affect safety and which can lead to leakage. This requirement can be
validated by:
— the calculation;
— the calculation and pressure-strengthening method, if allowed;
— the calculation and experimental method.
6.2 Load during the pressure test
The load exerted during the pressure test shall be calculated with Formula (1):
( )
pp≥ 13, + 1 𝑝𝑝 ≥ 1,3𝑝𝑝 + 1  baror (1)
( )
T s
Ts
where
p is the test pressure (in bar);
T
P is the maximum allowable pressure (in bar);
s
+1 is the allowance for external vacuum (in bar).
p is the test pressure (in bar);
T
P is the maximum allowable pressure (in bar);
s
+1 is the allowance for external vacuum (in bar).
7 Chemical effects
Due to operating temperatures and the materials of construction, the possibility of chemical action on the
inner surfaces in contact with the cryogenic fluids can be neglected.
Due to the fact that the inner vessel is inside an evacuated outer jacket, neither external corrosion of the
inner vessel, nor corrosion on the inner surfaces of the outer jacket will occur. Therefore, inspection
openings are not required in the inner vessel or the outer jacket.
Corrosion allowance is also not required on surfaces in contact with the operating fluid or exposed to the
vacuum interspace between the inner vessel and the outer jacket.
The material and the protection for the surfaces exposed to the atmosphere shall be suitable for intended
use (e.g. resistant to industrial and marine atmospheres).
8 Thermal conditions
The following thermal conditions shall be taken into account:
— for the inner vessel and its associated equipment, the full range of temperature expected;
— for the outer jacket and equipment thereof (other than equipment covered in Clause 7):
— a minimum working temperature of −20 °C;
— a maximum working temperature of 50 °C.
NOTE 1 Some locations require lower minimum working temperature e.g. –40 °C and/or higher maximum
working temperature, e.g. +65 °C.
NOTE 2 This does not apply if the jacket is designed for a lower temperature to be marked on the nameplate.
9 Materials
9.1 Selection of materials
9.1.1 Materials which are, or can be, in contact with cryogenic fluids shall be in accordance with
ISO 21010.
9.1.2 Materials used at low temperatures shall follow the requirements of the relevant partsclauses of
ISO 21028-1 and ISO 21028-2; for non-metallic materials, low-temperature suitability shall be validated
by an experimental method, taking into account operating temperatures.
9.1.3 The base materials, listed in Annex G, subject to meeting the extra requirements given in Clauses 5
to 16, are suitable for and may be employed in the manufacture of the cryogenic vessels, in conformance
with this document.
9.2 Inspection documentation
9.2.1 The material according to ISO 21028-1 and ISO 21028-2 shall be declared by an inspection
certificate 3.1 in accordance with ISO 10474:2013, 5.1.
9.2.2 The material manufactured to a recognized International Standard shall meet the testing
requirements of ISO 21028-1 and ISO 21028-2 and shall be declared by an inspection certificate 3.1 in
accordance with ISO 10474:2013, 5.1.
9.2.3 The delivery of material which is not manufactured to a recognized International Standard shall
be guaranteed by an inspection certificate 3.2 in accordance with ISO 10474:2013, 5.2 confirming that
the material fulfils the requirements in 9.1. The material manufacturer shall follow a recognized
International Standard for processing and establishing the guaranteed material properties.
9.2.4 The outer jacket and the equipment not subjected to low temperature shall be manufactured from
material suitable for the intended service.
10 Design
10.1 Design options
10.1.1 General
The design shall be carried out in accordance with one of the options given in 10.1.2, 10.1.3 or 10.1.4.
Metallic materials used at cryogenic temperatures shall meet the requirements of the relevant clauses of
ISO 21028-1 and ISO 21028-2.
In the case of 9 % Ni steel, the additional requirements in Annex C shall be satisfied.
10.1.2 Design by calculation
Calculation of all pressure-bearing and load-bearing components shall be carried out. The pressure part
thicknesses of the inner vessel and outer jacket shall not be less than required by 10.3. Additional
calculations are required to ensure the design is satisfactory for the operating conditions including an
allowance for dynamic loads.
10.1.3 Design by calculation and pressure strengthening
The pressure-retaining capability of inner vessels manufactured from austenitic stainless steel,
strengthened by pressure, shall be calculated in accordance with Annex D.
10.1.4 Design of components by calculation supplemented with experimental methods
Where it is not possible to design non-inner vessel components by calculation alone, planned and
controlled experimental means may be used provided that the results confirm the safety factors required
in 10.3. An example is the application of strain gauges to assess stress levels.
10.2 Common design requirements
10.2.1 General
The requirements of 10.2.2 to 10.2.7 are applicable to all vessels irrespective of the design option used.
In the event of an increase in at least one of the following parameters, the initial design process shall be
repeated to take account of these modifications:
— maximum allowable pressure;
— specific mass (density) of the densest gas for which the vessel is designed;
— maximum tare weight of the inner vessel;
— nominal length and/or diameter of the inner shell.
The initial design process shall be repeated also in the event of any change relative to:
— the type of material or grade (e.g. stainless steel to aluminium);
— the fundamental shape;
— the decrease in the minimum mechanical properties of the material being used;
— the modification of the design of an assembly method concerning any part under stress, particularly
as far as the support systems between the inner vessel and the outer jacket or the inner vessel itself
or the protective frame, if any, are concerned.
10.2.2 Design specification
To enable the design to be prepared, the following information which defines a vessel type shall be
available:
— maximum allowable pressure;
— fluids intended to be contained;
— gross volume of the inner vessel;
— dimensions and allowable weight, taking into account characteristics of the vehicle;
— location of fastening points and loads allowable on these points;
— filling and emptying rate;
— range of ambient temperature, if different from Clause 8;
— transportation mode (see Table 2 and Table 3).
A design document in the form of drawings with text, if any, shall be prepared. It shall contain the
information given above plus the following where applicable:
— definition of which components are designed by calculation, by pressure strengthening, by
experiment;
— drawings with dimensions and thicknesses of load-bearing components;
— specification of all load-bearing materials including grade, class, temper, testing, etc., as relevant;
— applicable mat
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